Pet Alternative Routes
Introduction
Generally, PET can be produced in two steps by one of two ways, called the DMT and the TPA processes, or the transesterfication and direct esterification routes, respectively. Since its commercialization in the 1950’s by DuPont, PET was predominantly synthesized out of DMT due to the fact that this monomer, compared to TPA, was relatively easily purified by distillation. Yet, since the 1960’s, purified TPA became available by the development of new technologies and gained a lot of importance as a monomer in polyester synthesis (Matsuzawa, K., 1976). The applications for PET include fibres and filaments, films, and bottlegrade chips. Modem plants are based on the TPA process and further, they incorporate direct product formation (fibres and filaments, films) by extruding the melt from the final polycondensation reactor.
Raw materials
First we shall contrast the DMT and the TPA processes. The main difference is the starting material. The older process used dimethyl terephthalate (DMT) and ethylene glycol (EG) as starting materials. This was because of the non availability of terephthalic acid of sufficient purity in the early years of polyester production. The newer industrial method uses purified terephthalic acid (TPA) instead of DMT and is called the TPA process. TPA was introduced on a commercial scale for the first time in the world by Amoco Corporation, USA in 1963. Since then, several plants for producing TPA have been set up all over the world. TPA has significant advantages over DMT and hence world over it has become the preferred raw material, in comparison with DMT, for polyester production.
The major advantages of TPA over DMT are as follows: * Weight of TPA required per ton of fibre is about 15% less than that of DMT. * Lower TPA: glycol ratios are possible as compared to DMT: glycol ratio. * Methanol as a by-product is not produced when TPA is used as in DMT use. Hence, no methanol recovery plant is needed. *
Generally, PET can be produced in two steps by one of two ways, called the DMT and the TPA processes, or the transesterfication and direct esterification routes, respectively. Since its commercialization in the 1950’s by DuPont, PET was predominantly synthesized out of DMT due to the fact that this monomer, compared to TPA, was relatively easily purified by distillation. Yet, since the 1960’s, purified TPA became available by the development of new technologies and gained a lot of importance as a monomer in polyester synthesis (Matsuzawa, K., 1976). The applications for PET include fibres and filaments, films, and bottlegrade chips. Modem plants are based on the TPA process and further, they incorporate direct product formation (fibres and filaments, films) by extruding the melt from the final polycondensation reactor.
Raw materials
First we shall contrast the DMT and the TPA processes. The main difference is the starting material. The older process used dimethyl terephthalate (DMT) and ethylene glycol (EG) as starting materials. This was because of the non availability of terephthalic acid of sufficient purity in the early years of polyester production. The newer industrial method uses purified terephthalic acid (TPA) instead of DMT and is called the TPA process. TPA was introduced on a commercial scale for the first time in the world by Amoco Corporation, USA in 1963. Since then, several plants for producing TPA have been set up all over the world. TPA has significant advantages over DMT and hence world over it has become the preferred raw material, in comparison with DMT, for polyester production.
The major advantages of TPA over DMT are as follows: * Weight of TPA required per ton of fibre is about 15% less than that of DMT. * Lower TPA: glycol ratios are possible as compared to DMT: glycol ratio. * Methanol as a by-product is not produced when TPA is used as in DMT use. Hence, no methanol recovery plant is needed. *